Proteins are the long polypeptide chains consisting of different forms amino acids. The kind of amino acids that are synthesized within our body are known as the non-essential amino acids. On the other hand, the amino acids that are not synthesized within the human body are called the essential amino acids. These are obtained from the dietary supplements.
There are total 20 amino acids, 11 amino acids are considered the non-essential amino acids and the remaining 9 are considered the essential amino acids. Each and every amino acid has a three- and one- letter code, for representing them in the polypeptide chains. The three- and one- code letter for the given amino acids are given as follows:
| Name of the amino acids | Three-letter code | One-letter code |
| Alanine | Ala | A |
| Proline | Pro | P |
| Leucine | Leu | L |
| Serine | Ser | S |
| Glutamic acid | Glu | E |
| Lysine | Lys | K |
| Aspartic acid | Asp | D |
| Glycine | Gly | G |
| Phenylalanine | Phe | F |
| Valine | Val | V |
| Threonine | Thr | T |
Thus, the one-letter code for polypeptide chain Glu-Leu-Pro-Asp-Val-Ala-Phe-Lys-Ser-Gly-Gly-Thr is ELPDVAFKSGGT.